It is known that oxide films with oriented crystallites generally exhibit improved properties. For example, Takayama, R. et al, Journal of Applied Physics, Vol. 65, (1989), pp 1666-1670, teaches the preparation of c-axis oriented lead zirconate titanate (PZT) thin films on (100)MgO substrates by rf-magnetron sputtering, which have relatively high pyroelectric coefficients.
The growth of oriented oxide films on semiconductor substrates is very attractive, but it is difficult to achieve in many cases due to film-substrate reaction and substrate oxidation during processing. This problem can be solved by the use of an intermediate layer between the substrate and the oxide film. Matsubara, S. et al, Journal or Applied Physics, Vol. 66, (1989), pp 5826-5832, teaches c-axis oriented PZT films on (100)Si having an epitaxial intermediate layer of MgAl.sub.2 O.sub.4 prepared by chemical vapor deposition (CVD).
Sinharoy, S., Thin Solid Films, Vol. 187, (1990), pp 231-243 teaches the use of one or more epitaxial alkaline earth fluoride buffer layers on semiconductors including GaAs to provide lattice matching. Tiwari, A. N. et al, Journal of Applied Physics, Vol. 71, (1992), pp. 5095-5098, teaches the use of epitaxial fluoride layers as a buffer for the growth of high-temperature superconducting oxides. Hung, L. S. et al, Applied Physics Letters, Vol. 60, (Jan. 13, 1992), pp. 201-203 teaches that with Si and GaAs substrates, BaF.sub.2 and Ca.sub.x Sr.sub.1-x F.sub.2 buffer layers have the advantages of process compatibility with both Si and GaAs, good film quality and low processing temperatures. Epitaxial alkaline earth fluoride buffer layers have the shortcoming of high reactivity with some oxides and deteriorated crystal qualities in oxygen.
Metal oxides such as ZrO.sub.2, PrO.sub.2, CeO.sub.2, Al.sub.2 O.sub.3, MgAl.sub.2 O.sub.4 and MgO have been reported to grow epitaxially on Si substrates. MgAl.sub.2 O.sub.4 has too high a deposition temperature for use with GaAs. Orientation of epitaxial metal oxide buffer layers matches the orientation of the substrate in some cases, but not in others. Inoue, T., Applied Physics Letters, Vol. 59, (1991), pp 3604-3606, teaches epitaxial growth of (111)CeO.sub.2 on (111)Si; but epitaxial growth of (110) CeO.sub.2 films on (100)Si. Osaka, Y. et al, Journal of Applied Physics, Vol. 63, (1988), pp 581-582; teaches epitaxial growth of (100)ZrO.sub.2 on (100)Si, but the growth of polycrystalline films on (111)Si, by the same technique. Fork, D. K. et al, Applied Physics Letters, Vol. 60, (1992), pp 1621-1623 teaches epitaxial growth of a (100) MgO buffer layer on (100) GaAs by using pulsed laser ablation of Mg metal in an oxygen ambient. Hung, L. S. et al, Applied Physics Letters, Vol. 60, (1992), pp 3129-3131, teaches epitaxial growth of a (110)MgO buffer layer on (100)GaAs using ultrahigh vacuum electron beam evaporation of MgO.
In some uses, it is also desirable to have an electrode between an oxide film and its substrate. To prepare an oxide film on Si having a desired orientation and an underlying electrode, it is highly desirable to have an epitaxial metal layer with good adhesion to the substrate and high resistance to oxidation. There are significant obstacles for growth of such epitaxial metal layers because of pronounced differences between semiconductors and metals in crystal structures and lattice parameters, and the relatively high reactivities of metals. Niwa, H. et al, Applied Physics Letters, Vol. 60, (1992), pp 2520-2521; teaches the epitaxial growth of (111)Al on (111)Si. Thangaraj, N. et al, Applied Physics Letters, Vol. 61, (1992), pp 37-39 teaches that the growth of (100)Al on (100)Si is difficult to achieve and the film on (100)Si is (110) oriented. Al has the shortcomings of being highly reactive to oxygen and forming a eutectic liquid with Si at 573.degree. C. Al is thus precluded from use as an underlying electrode for oriented perovskite-type oxides. Pt has a high stability in oxygen at elevated temperatures, but reacts with Si to form Pt.sub.2 Si at temperatures as low as 200.degree. C. This shortcoming can be avoided by depositing Pt on a SiO.sub.2 layer thermally grown on Si, however, the deposited Pt is polycrystalline and is subject to adhesion problems. Trolier, R. et al, Journal of Crystal Growth, Vol. 98, (1989), pp 469-479 teaches the growth of [100]-oriented Pt on (100) Si using graphoepitaxy, however, this process requires prolonged annealing at elevated temperatures for crystal alignment and produces Pt films which exhibit poor crystal quality and deteriorated surface morphology.
It is therefore highly desirable to prepare structures having an epitaxial metal film, an intermediate layer, and a semiconductor substrate, in which the metal layer has good adhesion and high resistance to oxidation.